What does it take to "reset" a 777?
 

Saturday night I should have been flying a BA 777 from San Diego to Heathrow but instead after a long delay the flight was canceled. Before we were deplaned I got to speak to the captain and he told me that there had been some information from one of the engines missing on the computer and although an engineer had cleared the plane, during the takeoff roll the warning had come up again and we couldn't depart. After trying lots of things the idea was to power off and on the computer which would take "about 10 minutes", so we all got off to wait. About an hour later the ground staff told us that the engineers were now "resetting the plane" and they'd keep us up to date. Another 90 minutes later we were told the flight was canceled as we had passed the 1am takeoff curfew.

So I'm curious how long should "resetting" the plane take ? Is it a 30 minute thing, a multi hour thing? The plane did eventually leave for Heathrow Sunday night (presumably empty) so whatever was causing the error must have been fixed but I'm just wondering if the engineers hadn't realised how long it would take, or there was a lot more going on.

A 'reset' of a 777 (or most aircraft) basically means depowering completely, then bringing it back up from the depowered 'cold' state.
10 minutes sounds about right for doing that.
Educated guess is that they thought they had a 'soft' fault that would be corrected by what is essentially a 'reboot'. But it turned out to be a 'hard' fault that required actual troubleshooting and replacement of the defective box.

I would guess the first power down and reboot didn't work so they tried it again, and again. With a limited number of options, spare parts and with a crew approaching their time on duty limits they probably did multiple resets, box swaps and various other trouble shooting tasks in vain. They may have even fixed the snag but not before the crew went out of hours.
It's frustrating as hell for all concerned but as safety is the priority, getting it right is paramount.

Many years ago I investigated a problem with 777 display of engine limits. I was eventually given data from one of the early flight test aircraft that explained the problem and I reported my findings. I don't think the problem was ever fixed.

Basic problem was that EEC was required to provide limits data to AIMS. Because of a system level requirements defect EEC stopped sending the data before AIMS was ready to receive it. It I remember correctly re-powering the aircraft did not fix the problem because every power up had the same timing and AIMS could not receive the required data.

I think the solution was to delay EEC power up until after AIMS power up was complete. There was an alternative work-around but I don't remember any details. I think it required some action on the MAT.

On the 777, we started getting engine limits from the EEC (aka FADEC) - prior to that, the limits were hard coded in EICAS, meaning that a simple change to an engine limit (which are not particularly uncommon) required an EICAS software roll (cost starts at seven figures to roll EICAS software). Hence the change in the 777 (and subsequent Boeing installations).
On Boeings, the EEC is not normally powered prior to engine start (putting the fuel switch to run or start switch to start provides aircraft power to the EEC since the PMA doesn't come alive until ~8% N2/N3) - and no one should ever be attempting an engine start before AIMS is fully booted and running. However, if someone leaves the EEC ground test power ON (contrary to SOP) (flight deck switches used for troubleshooting without have to run the engine), then the scenario you describe is a possibility. The cure is to turn off EEC ground test power, and follow the SOP to not power up the EEC until after AIMS is fully up and running.

Thanks for that additional information. I may have known all that when I was investigating the reported problem but it was a while ago. What I do remember is that the flight test data showed simultaneous initiation of AIMS and EEC power up and the data transfer timing issue that I described.

Perhaps that data was given to me because it represented the special case that produced the problem and not because it was typical of revenue operations.

Thanks for the insights. We were originally delayed 45 minutes for an engine test which the captain said couldn't be done with passengers on board but had satisfied the engineer and they had been signed off to depart. But whatever it was came back on the takeoff roll, which can't have been more than 100 ft before the abort. Definitely frustrating but like they say better to be on the ground......

I doubt I'm in any position to diagnose the problem but can you say what data was missing and what the alert was?